In multiple blood bags and the like, it is desirable to provide an initial seal in the tubing between the multiple blood bags which can be opened without breaking the sterility within the system. This has been done in the past by various types of pointed cannulas positioned within the tubing itself and manipulated from the outside, to penetrate a diaphragm or membrane closing off the tubing. Also, a ball may be wedged into the tubing between the blood bags, to be removed by squeezing it out of the tubing to drop into the bag for opening of the valve.
Other breakaway structures within the tubing are known, so that, by manipulation from outside of the tubing, a rigid, closed-end tubular structure is broken in the middle to open a flow channel through the tubing. These structures, however, exhibit the disadvantage that they cannot be resealed once they have been opened. Also, they exhibit some difficulty of manipulation and use.